Nuclear magnetic resonance study of atomic motions in vanadium

Abstract

Atomic motions in solid vanadium have been investigated by means of NMR. For that purpose, the Zeeman spin-lattice relaxation time T 1, the rotating-frame spin-lattice relaxation time T 1 ρ , and the Knight shift K of 51V in polycrystalline vanadium have been measured as a function of temperature in the range between 300 and 2000 K. At all temperatures, the relaxation time T 1 is mainly determined by electronic contributions leading to a temperature-dependent expression for the Korringa relation T 1, T · K 2. In contrast to the T 1,-data, two pronounced peaks in the relaxation rate T −1 1 ρ at about 750 and 1600 K, respectively, are observed. The peak at 750 K arises from fluctuations in the nuclear quadrupolar interaction between vanadium and interstitially migrating oxygen whereas the maximum at 1600 K is caused by fluctuations in the nuclear dipole interaction due to atomic self-diffusion. From the low-temperature data, the diffusivity of oxygen is determined to be D 1, = 3.2·10 −6exp(−0.73 eV/ kT)cm 2/s. By comparing the self-diffusion contribution to the relaxation rate with the tracer measurements of Pelleg, the correlation factor ∝ was found to be ∝= 0.77 ±0.11 consistent with a monovacancy diffusion mechanism. The uncorrelated self-diffusion coefficient was obtained as D SD = 0.14 exp(−3.09 eV/ kT)cm 2/s.